Zinc (Zn) and iron (Fe) deficiencies are well-documented public health issue affecting nearly half of the world population. Developing countries are among the worst affected from Zn and Fe deficiencies which result in number of serious health complications, such as impairments in brain function and mental development, high susceptibility to deadly infectious disease and high risk for anemia. Recent reports indicate that, for example, Zn deficiency is responsible for death of nearly 450 000 children under 5-years old, annually. Very low concentrations and poor bioavailability of Zn and Fe in the commonly consumed foods seem to be the main reason for widespread occurrence of micronutrient deficiencies in human populations. Cereal-based foods are most commonly consumed foods and contribute up to 75 % of the daily calorie intake in the rural parts of the developing countries. Zinc and Fe deficiencies are also common micronutrient deficiencies in agricultural soils limiting both crop production and nutritional quality
Breeding new cereal genotypes with high genetic capacity for grain accumulation of micronutrients is widely accepted and most sustainable solution to the problem. There are impressive progresses in breeding new genotypes for high micronutrient density. However, the breeding approach is a long-term process and may be affected from very low chemical solubility of Zn and Fe in soils due to high pH and low organic matter. Agronomy-related approaches offer short-term and complementary solutions to the Zn and Fe deficiency in human health and crop production. Soil amendments contributing to solubility of Zn and Fe in soil solution, cereal-legume intercropping systems, and soil and foliar application of micronutrient-containing fertilizers are well-documented agronomic tools which contribute to root uptake, shoot and grain accumulation of Fe and Zn.
Fertilizer strategy is a simple and effective agronomic practice to contribute grain concentrations of micronutrients. Increasing number of evidence is available showing that soil and especially foliar application of Zn fertilizers results in impressive enhancements in grain Zn concentration. In contrast, soil and foliar application of Fe fertilizers is not effective in increasing grain Fe concentration. In wheat, foliar application of ZnSO4 at later growth stages seems to be more effective in enhancing grain Zn concentration than the application at earlier growth stages. Late foliar application of Zn is also effective in higher accumulation of Zn in the endosperm part of grains compared to earlier application. Enrichment of commonly soil-applied fertilizers like urea with Zn seems to be also very helpful strategy in improving grain Zn concentration. Recently published results indicate that soil and/or foliar application of nitrogen fertilizers improve both root uptake and grain accumulation of Fe and Zn.
The results available indicate high potential of agronomic approaches for improving grain Zn and Fe concentrations. Agronomic practices mentioned are simple and easily applicable in many target countries with high incidence of micronutrient deficiencies. Combination of agronomic practices with breeding approach will ensure the plants to maximize grain accumulation of micronutrients. This paper will also summarize the results of a recently initiated global zinc fertilizer project in 10 countries under HarvestPlus program (www.harvestzinc.org).